JP5437801B2 - Multilayer sealant film - Google Patents

Description

  The present invention claims priority from US Provisional Application No. 60 / 831,016, filed July 14, 2006, the entire specification of which application is incorporated herein by reference.

  Polylactic acid (PLA) is a highly biodegradable polymer and is obtained from natural raw materials such as corn. The use of PLA for the production of food packaging trays is increasing, which is because, at least in part, polylactic acid is readily biodegradable, and trays made from polylactic acid are highly This is due to having a high oxygen content and moisture transmission rate. However, trays made from PLA tend to soften and deform at temperatures as low as 104 ° F (40 ° C). Because of this drawback, critical requirements for lid films for use in PLA trays are low heat seal temperatures (around 200 ° F, ie around 93 ° C), short residence times (less than 2 seconds) It must be formed with. The conventional sealant film does not heat seal (heat fusion) to the PLA tray at a sufficiently low temperature, or the heat seal strength decreases when it is long after sealing. Coextruded PLA films with one amorphous PLA layer and one crystalline PLA layer can be sealed to PLA trays at low temperatures, but such films are typically very brittle and easily Rips and does not fit well on packaging lines, especially high speed packaging lines.

U.S. Pat.No. 4,375,494

  As mentioned above, it would be advantageous to provide a lidding film that satisfies both the sealing performance requirements for use in PLA trays and the film processing performance required for practical normal use.

In one aspect, the present invention provides:
a) a substrate comprising a polymeric base layer;
b) providing a multilayer film comprising a heat seal layer comprising a PLA polymer on the substrate. The heat seal layer further includes an adhesion promoter dispersed therein, or the substrate is between and adjacent to the polymer base layer and the heat seal layer. An adhesion promoter is further included in the layer on the surface of the base layer.

  In another aspect, the present invention is a sealed container comprising a container having an opening, the opening having a heat seal layer of the film as described above using the multilayer film according to claim 1. A sealed container is provided which is sealed with.

In yet another aspect, the present invention provides a method for producing a multilayer film. This method
a) applying a coating solution to a substrate comprising a polymeric base layer,
The coating solution includes a solvent and a PLA polymer;
The coating solution further comprises an adhesion promoter, or the substrate further comprises an adhesion promoter in a layer on the surface of the polymeric base layer for receiving the coating solution, A process that is either
b) removing the solvent to form a heat seal layer containing the PLA polymer.

  In a further aspect, the present invention provides a coating composition comprising a PLA polymer, a copolyester, and a solvent.

  The inventor has realized that it is very difficult to achieve adequately adherent PLA polymers to polyethylene terephthalate (PET) and many other substrates using methods known prior to the present invention. To address this and other problems, the multilayer film of the present invention comprises a substrate comprising a polymeric base layer and a heat seal layer comprising a PLA polymer on the substrate. One or both of the heat seal layer and the substrate further comprises an adhesion promoter that enhances the adhesion between the PLA polymer and the polymeric base layer while providing good low temperature heat seal properties. To maintain. Unless otherwise specified, the term “PLA polymer” as used herein includes homopolymers of lactic acid and copolymers of lactic acid containing at least 30 mol% lactic acid repeat units. If the substrate includes the adhesion promoter as a layer, this layer can be formed in-line during the manufacturing process of the polymeric base layer or offline after the polymeric base layer is manufactured. In general, the polymeric material (ie, “heat sealable” polymer) that will be used in the heat seal layer is at least 50 ° F., typically at least 100 ° F. more typically than the softening temperature of the polymeric base layer. In particular, it is a thermoplastic polymer having a softening temperature that is at least 150 ° F lower. The softening temperature is preferably higher than 75 ° F.

  When the adhesion promoter is dispersed in the heat seal layer, the dispersion can take the form of a uniform solution, or the heat seal layer can be composed of a polymeric dispersed phase and a polymeric continuous phase having different compositions. Can be included. In some embodiments, the adhesion promoter accounts for more than 50% by weight of one of these phases and the PLA polymer accounts for more than 50% by weight of the other of these phases. The adhesion promoter may be dispersed in the PLA polymer or vice versa. It is believed that the cloudy appearance present in the heat seal layer of some embodiments of the present invention indicates the presence of different composition polymer phases. One typical formulation that provides such an appearance and good heat seal performance after drying the substrate is an amorphous PLA polymer (PLA 4060D, D, L-polylactic acid polymer from NatureWorks LLC (Minnetonka, Minn.)). 30% and 70% copolyester (azeline acid / terephthalic acid / ethylene glycol, 45/55/100 molar equivalent).

  The inventor has carefully selected the adhesion promoter so that the PLA is not deformed while the PLA, such as a tray, is at a sufficiently low temperature to provide good adhesion between the PLA polymer layer and the substrate. It has been found that it is possible to produce a multilayer film that can seal the product. Furthermore, these films typically exhibit excellent processability in packaging lines, at least in part due to the presence of a mechanically strong polymeric base layer.

  Any thickness of multilayer film can be used in accordance with the present invention. Typically, the polymeric base layer may be in the range of 12 to 120 microns. The heat seal layer is typically in the range of 0.5 to 20 microns, more typically 2.0 to 10 microns. These relatively thin heat seal layers can typically be produced by solution coating and can be difficult to achieve by other methods such as extrusion coating or coextrusion coating. . The disadvantage of extruded PLA polymers is that the polymers need to be dried beforehand to prevent thermal degradation. This special step can be eliminated if the PLA polymer is applied by solution coating under typical conditions (ie, processing temperatures below the thermal denaturation temperature of the PLA polymer). If a separate adhesion promoting layer is present between the PLA polymer and the polymeric base layer, the adhesion promoting layer is typically in the range of 0.02 to 5 microns thick.

  When the heat seal layer includes an adhesion promoter dissolved or dispersed therein, the amount of adhesion promoter is typically at least 1% by weight of the total weight of the promoter and PLA monomer. Typically at least 10 wt%, most typically at least 20 wt%, or at least 30 wt%. This amount is typically up to 90% by weight, more typically up to 70% by weight and most typically up to 40% by weight. In embodiments of the invention where the heat seal layer is required to be relatively transparent (not cloudy), the relative amount of adhesion promoter to PLA polymer may be preferred to be somewhat lower. . For example, the amount of adhesion promoter is typically at least 20%, more typically at least 30%, most typically at least 40% by weight of the total weight of the promoter and PLA monomer . This amount is typically up to 60% by weight, more typically up to 50% by weight. If it is desired to avoid the formation of water droplets on the surface of the film when used in an environment where such formation is encouraged (eg, packaging of frozen foods), it is further described below. Thus, an antifogging agent can also be used. The components that make up the multilayer film are discussed in further detail below, and then describe how the film is made and some typical uses of the film.

[Heat seal layer]
The heat seal layer includes at least one PLA polymer. Suitable PLA polymer types for use in accordance with the present invention may be any type known in the art, including homopolymers and copolymers of lactic acid. Suitable copolymers include the formula:
HOC (R ¹ ) (R ² ) (CH ₂ ) _n COOH
(Wherein R ¹ and R ² are each independently H or a substituted or unsubstituted C _{1 to} C ₅ group, and n is an integer of 0 to 10)
These copolymers are included. The PLA polymer may be amorphous (ie, at least 90% amorphous as measured by differential scanning calorimetry), or the PLA polymer may be substantially crystalline. It is typically up to 50% crystalline and more typically up to 20% crystalline. PLA polymer may be a homopolymer of lactic acid and is one of the following morphologically distinct polymers: D-polylactic acid, L-polylactic acid, D, L-polylactic acid, and meso-polylactic acid It may be above. D-polylactic acid and L-polylactic acid are correspondingly pure enantiomeric polymers and optically active polymers. D, L-polylactic acid is produced from racemic lactic acid. That is, D, L-polylactic acid is a copolymer of D-polylactic acid and L-polylactic acid having a well-defined conformation of D- and L-polylactic acid units. Meso-polylactic acid is a random copolymer of equimolar D-polylactic acid and L-polylactic acid. It is known that the morphology of PLA homopolymer is governed by the ratio of D isomer to L isomer in the polymer backbone. Typically, the higher the D-lactic acid content, the lower the crystallinity of the polymer.

  Any known polymerization method, such as polycondensation and ring-opening polymerization, can be employed to polymerize lactic acid. In the polycondensation method, for example, L-lactic acid, D-lactic acid, or a mixture thereof is directly subjected to a dehydration polycondensation reaction known in the art. In the ring-opening polymerization method, lactide (that is, a cyclic dimer of lactic acid) is subjected to a polymerization reaction in the presence of a catalyst to form polylactic acid. The lactide may be a dimer of L-lactic acid, a dimer of D-lactic acid, or a mixed dimer of L-lactic acid and D-lactic acid. These isomers can be mixed and polymerized to obtain polylactic acid having any desired composition and crystallinity.

  Small amounts of chain extenders (eg, diisocyanate compounds, epoxy compounds, or acid anhydrides) can be used to increase the molecular weight of the PLA polymer. The polymer may be in any molecular weight range, but typically the weight average molecular weight is in the range of 60,000 to 1,000,000 daltons. Typically, if the molecular weight is less than 60,000, appropriate physical properties may not be obtained. On the other hand, if the molecular weight is higher than 1,000,000, the melt viscosity becomes excessively high and the moldability deteriorates.

  The PLA polymer may be a copolymer of lactic acid and one or more comonomers. Such copolymers, when present, comprise a total of less than 50 mole percent, typically less than 30 mole percent, more typically less than 10 mole percent of the PLA polymer. Examples of such comonomers include caprolactone; hydroxycarboxylic acids (eg, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, and 6-hydroxycaproic acid); polyols (eg, ethylene Glycols, propylene glycol, butanediol, neopentyl glycol, poly (ethylene glycol), glycerol, and pentaerythritol); and polybasic acids (eg, succinic acid, adipic acid, sebacic acid, fumaric acid, terephthalic acid, isophthalic acid) 2,6-naphthalenedicarboxylic acid, 5-sodiumoxysulfonylisophthalic acid, and 5-tetrabutylphosphonium sulfoisophthalate). In some embodiments of the invention, the comonomer is preferably biodegradable (if present).

  In some embodiments of the invention, the film includes an antifogging agent to reduce or eliminate the formation of haze on the inner surface of the film due to the formation of water droplets. The antifogging agent is dispersed within the heat seal layer and / or is present on the surface of the heat seal layer opposite the substrate. In some embodiments, the antifogging agent may be part of a formulation used to form the heat seal layer, the antifogging agent may remain widely dispersed in the heat seal layer, Alternatively, the antifogging agent may coat the surface. Alternatively, the antifogging agent can be applied directly to the surface of the heat seal layer by dipping, spraying or coating (typically coating from a solvent). Examples of suitable anti-fogging agents include alkoxylated fatty ethers (eg ATMER® 502), sorbitan esters (eg ATMER® 103), other known nonionic, anionic, And cationic surfactants (eg, polyalkylene fatty acid esters, alkoxylated phenols, mixed mono-, di- or tri-glycerides, fatty acid esters of polyhydroxy alcohols, other polyalkoxylated compounds, etc.) included. ATMER® products are available from Ciba Specialty Chemical (Tarrytown, NY). When included in the heat seal layer, the anti-fogging agent typically comprises about 0.1% to 15%, more typically about 0.5% to 10% by weight of the heat seal layer. When applied directly to the surface of the heat seal layer, the amount of anti-fogging agent is typically about 0.1% to 5% by weight of the heat seal layer, more typically about 0.1% to 1%. It is in the range of wt%.

  The heat seal layer may include inorganic particles (such as silica) and / or slip agents (such as wax) and / or polytetrafluoroethylene dispersion. For some applications, an antioxidant may be included. In some embodiments, the heat seal layer can be free of plasticizers (eg, polyglycols or polyethers, or esters thereof), tackifiers, and / or inorganic fillers. The heat seal layer may also be free of aliphatic polyesters other than PLA polymers in some embodiments.

[Adhesion promoter]
As used herein, the term “adhesion promoter” is added to the PLA polymer in the heat seal layer, or when used as an intermediate layer between the heat seal layer and the polymeric base layer, the method in the Examples section. means a material that provides a heat seal strength of at least 200 g / inch measured according to (ii). This strength is typically at least 300 g / inch and more typically at least 400 g / inch. Preferably, the adhesion promoter provides a cohesive failure state when peeling the film according to method (ii), each heat seal layer remains in the polymeric base layer, and separation occurs within the fused heat seal layer. Suitable adhesion promoters include, but are not limited to, ethylene copolymers such as EVA (ethylene-vinyl acetate) and EMA (ethylene-methyl acrylate), and tackifying resins such as rosin esters. included.

In some embodiments, the adhesion promoter comprises a copolyester resin. As used herein, the term “copolyester” refers to at least one (preferably one) aromatic dicarboxylic acid and at least one (preferably one) aliphatic dicarboxylic acid, or lower alkyl diesters thereof ( Means a polyester derived from one or two glycols from up to 14 alkyl diesters of carbon atoms. The formation of the copolyester can be conveniently effected by known methods of condensation or transesterification, generally at temperatures up to about 275 ° C. Exemplary aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, and 2,5-, 2,6-, or 2,7-naphthalenedicarboxylic acid. Representative aliphatic dicarboxylic acids are saturated aliphatic dicarboxylic acids of the general formula C _n H _2n (COOH) ₂ where n is 2 to 8 (eg, succinic acid, sebacic acid, adipic acid, azelain). Acid, suberic acid, or pimelic acid), sebacic acid, adipic acid, and azelaic acid are preferred, and azelaic acid is more preferred.

  In some embodiments, the polyester contains less than 90% aromatic dicarboxylic acid (such as terephthalic acid) and at least 10% aliphatic dicarboxylic acid (% is the total diacid content of the polyester). Mole percent). Typically, the concentration of aromatic dicarboxylic acid is at least 55 mol% and may be 60 mol% or more. This concentration is typically about 80 mol% or less, more typically 70 wt% or less, and most typically 65 mol% or less, based on the dicarboxylic acid component of the copolyester. The concentration of the aliphatic dicarboxylic acid in the copolyester is typically at least 20 mol%, more typically at least 35 mol%, typically the highest, based on the dicarboxylic acid component in the copolyester. Up to 45 mol%. Expressed on a weight basis, the relative amounts of aromatic and aliphatic dicarboxylic acids are somewhat dependent on their respective molecular weights, but are typically at least 55% by weight aromatic dicarboxylic acid and at least 45% by weight. Aliphatic dicarboxylic acids are present.

  Suitable glycols include aliphatic glycols such as alkylene glycols. In addition, suitable glycols include aliphatic diols (eg, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2,2 -Dimethyl-1,3-propanediol, neopentyl glycol, and 1,6-hexanediol). Ethylene glycol or 1,4-butanediol is typically used. The copolyester is typically at least 50% amorphous and may be completely amorphous (ie, at least 90% amorphous as measured by differential scanning calorimetry).

  As described above, the copolyester may be dispersed with the PLA polymer in the heat seal layer and / or form part of the substrate (ie, form a layer on the polymeric base layer). Also good.

[Polymeric base layer]
The polymeric base layer may include any film-forming polymer known in the art, provided that it is mechanically stronger than a film made solely from PLA homopolymer. Examples include, but are not limited to, polyester films, nylon films, films made of polyethylene or ethylene copolymers, polypropylene films, and films made of reinforced PLA materials.

  In some embodiments of the present invention, the polymeric base layer comprises a linear polyester layer, typically a biaxially oriented linear polyester layer. Typically, the linear polyester has an intrinsic viscosity of about 0.5 to about 0.8, most typically about 0.6. Examples of polyester films include biaxially oriented polyethylene terephthalate (PET) film and biaxially oriented polyethylene naphthalate (PEN) film.

  Particularly useful is polyethylene terephthalate that is biaxially oriented and heat set. Such materials are well known in the art and are described, for example, in Stokes US Pat. No. 4,375,494, incorporated herein by reference.

  Production techniques for polyethylene terephthalate polymers are well known to those skilled in the art, and are disclosed in, for example, many documents such as Encyclopedia of Polymer Science and Engineering, 2nd. Ed., Vol. 12, Wiley, NY, pp. 1-313. ing. The polymer is typically obtained by condensing a suitable dicarboxylic acid or its lower alkyl diester with ethylene glycol. Polyethylene terephthalate is formed from terephthalic acid or its ester, and polyethylene naphthalate is formed from 2,6-naphthalenedicarboxylic acid or its ester.

  When a co-extruded bi-layer polyester / copolyester film is used as the substrate on which the PLA is coated, the bi-layer film composite can be multi-stage extruded with multiple orifice dies or co-extruded with composite layers (e.g., , Widely described in U.S. Pat. No. 3,871,947), followed by molecular orientation by stretching in one or two directions, and heat-set methods. A convenient method and apparatus for coextrusion, known as single channel coextrusion, is described in U.S. Pat. No. 4,165,210 and British Patent Specification 1111507. This method simultaneously extrudes the first and second polyester streams from two different extruders, directs these two streams through the tube to the extrusion die manifold, and further converts the two polyesters into two Film composites are produced by extruding together through the die under laminar flow conditions that occupy different regions of the flow without mixing.

  Biaxial orientation of the polyethylene terephthalate portion of the film composite can be achieved by stretching the composite sequentially in two mutually orthogonal directions, typically in the range of 78 ° C to 125 ° C. In general, the conditions for stretching the composite can serve to partially crystallize the first thermal adhesive layer. Furthermore, in such a case, it is preferable to heat-set the film composite at a temperature higher than the crystal melting temperature of the first thermoadhesive layer but lower than the crystal melting temperature of the polyethylene terephthalate portion under the dimension constraint conditions. The composite is then allowed to cool or cool so that the first thermal adhesive layer is essentially amorphous while the PET portion remains highly crystalline. Therefore, following the stretching operation, it is preferable to heat set at a temperature in the range of 150 ° C. to 250 ° C. under dimensional constraint conditions. A convenient stretching and heat setting method is described in US Pat. No. 3,107,139. The coextruded film composite described herein, incorporating a polyester base layer, and a copolyester layer on the polyester base layer, is manufactured under the name MELINEX® 301H by DuPont Teijin Films ( Wilmington, DE) is commercially available. As described above, they can be coated with PLA polymers in accordance with the present invention with or without additional copolyesters in the PLA coating composition.

[Manufacture of multilayer sealant film]
The multilayer film of the present invention can be produced by coating a polymeric substrate with a PLA polymer solution (optionally also containing an adhesion promoter) in a solvent. As used herein, the term “solvent” means a volatile carrier for one or both of the PLA polymer and adhesion promoter, and the resulting mixture is an emulsion, microemulsion, or other dispersion. It may be a complete solution in a strict sense. Suitable solvents include but are not limited to water, tetrahydrofuran, methyl ethyl ketone, toluene and the like. When water is used as a solvent, an emulsifier can be used to produce an emulsion or microemulsion.

  When the PLA polymer is used alone, the side of the substrate on which the PLA polymer is coated must have an adhesion promoting layer. For example, a polyester film having a solvent-coated copolyester layer can be used, but a co-extruded multilayer (typically two-layer) polyester / copolyester film can also be used. In either case, the PLA polymer is then coated onto the substrate to obtain a multilayer film.

  Coating can be done by any method known in the art, for example, methods involving inversion metrology and gravure. The inventor has found that by using a solvent coating method, it is possible to produce a multilayer film having a relatively thin heat seal layer (eg, 0.5-20 microns). Such relatively thin layers are often difficult to obtain by other methods such as extrusion or coextrusion coating. The present invention thus makes it possible to obtain multilayer films having a high area-to-weight ratio compared to other structures produced by other methods, such as lamination or extrusion coating. In addition, a thinner heat seal layer also provides a more easily removable (peelable) seal that is advantageous in some applications (eg, sealed packaged food containers).

[Use of multilayer sealant film]
As described above, the film of the present invention can be used as a film for covering a container, particularly in a closed container (for example, a PLA tray). Typically, such trays or other vessels are made of polylactic acid homopolymers, but are not limited to lactic acid and comonomers (including, but not limited to, the comonomers mentioned above for PLA polymers used in heat seal layers). Copolymers) may be used in accordance with the present invention. However, other types of containers can be sealed with these films, and such use is also envisaged in the present invention. Essentially any container with an opening can be sealed with the multilayer film of the present invention having a heat seal layer on the side of the film.

  The following test methods are used in the examples below.

[Sample test method]
(I) The heat seal strength to the tray is measured as follows. The film is heat sealed to the PLA tray container sheet on the heat sealer with its heat seal layer at 200 ° F. and 35 psi pressure for 0.5 seconds. The required load to cut a sealed film and tray strip (25 mm wide) at 90 ° to the seal and peel off the seal using the Instron operating at a crosshead speed of 0.25 m / min Measure. This procedure is usually repeated 4 times and the average of the 5 results is calculated.

  (Ii) The heat seal strength of the composite film to itself is measured as follows. The heat seal layers of the two film samples are placed together and heated at 230 ° F. for 0.5 seconds under a pressure of 35 psi. Allow the sealed film to cool to room temperature and cut the sealed composite into 25 mm wide strips. Heat seal strength is determined by measuring the force per unit seal width required under linear tension to peel the layers of film at a crosshead speed of 0.25 m / min.

  (Iii) The crystallinity ratio can be measured by differential scanning calorimetry. A 5 mg sample is taken from the film and heated from 0 ° C. to 300 ° C. at 80 ° C./min with a Perkin Elmer DSC7B differential scanning calorimeter. The crystallinity ratio assumes that crystallinity is present in all samples.

[Sample preparation]
Preparation of Coating Solution # 1: 99 g PLA 4060D (low crystalline D, L-polylactic acid polymer purchased from NatureWorks LLC (Minnetonka, Minn.)), 0.5 g KEMAMIDE E antiblocking agent (purchased from Witco), and SYLOID 244 slip agent (purchased from WR Grace) was added to 500 g of tetrahydrofuran (THF). This mixture was stirred for 30 minutes to obtain Coating Solution # 1.

  Preparation of Coating Solution # 2: 69 g PLA 4060D, 30 g azelaic acid / terephthalic acid / ethylene glycol copolyester (45/55/100 molar equivalent), 0.5 g KEMAMIDE E, and 0.5 g SYLOID 244 To 400 g of tetrahydrofuran (THF). This mixture was stirred for 30 minutes to give Coating Solution # 2.

Sample 1: Coating solution # 1 was coated on 92 gauge MYLAR E film (biaxially oriented polyethylene terephthalate film manufactured by DuPont Teijin Films) by a progressive coating method. Adjust the roll gap was achieved a dry coating weight of 8 g / m ^2. The wet coating was dried at 100 ° C. for 1 minute.

Sample 2: Coating solution # 1 was coated on a MYLAR 100OL film (biaxially oriented polyethylene terephthalate film with a copolyester layer manufactured by DuPont Teijin Films) by a progressive coating method. Adjust the roll gap was achieved a dry coating weight of 8 g / m ^2. The wet coating was dried at 100 ° C. for 1 minute.

Sample 3: Coating solution # 2 was coated on 92 gauge MYLAR E film (DuPont Teijin Films) by a progressive coating method. Adjust the roll gap was achieved a dry coating weight of 8 g / m ^2. The wet coating was dried at 100 ° C. for 1 minute.

Sample 4: Coating solution # 2 was coated on a MYLAR 100OL film (DuPont Teijin Films) by a progressive coating method. Adjust the roll gap was achieved a dry coating weight of 8 g / m ^2. The wet coating was dried at 100 ° C. for 1 minute.

The films prepared in Samples 1-4 were heat sealed to the PLA tray manufacturing stock and the film itself, respectively, according to methods (i) and (ii) described above. The resulting heat seal strength is shown in g / inch in the table below.

  By comparing Samples 1 and 2, the heat seal performance of the heat seal layer containing only PLA (Sample 2) on the base film having the copolyester intermediate layer is the base without the intermediate copolyester layer. It can be seen that the heat seal performance of the heat seal layer (sample 1) containing only PLA on the film is better. Further, by comparing Samples 1 and 3, when no intermediate copolyester layer is present, adding a copolyester to the PLA heat seal layer (Sample 3) results in a heat seal layer containing only PLA (Sample 1). It can be seen that high heat seal strength can be obtained. Finally, by comparing sample 4 with either sample 2 or sample 3, by including a copolyester in the PLA heat seal layer and by including the copolyester as an intermediate layer, respectively It turns out that good performance is brought about.

  Although the invention is illustrated and described herein with reference to specific embodiments, it is not intended that the invention be limited to these apparent details. Rather, various modifications may be made in the claims and details within their scope without departing from the invention.

Claims (13)

A method for producing a multilayer film for use in sealing a container,
a) applying a coating solution to a substrate comprising a polymeric base layer,
The coating solution includes a solvent and a PLA polymer;
Either the coating solution further comprises an adhesion promoter, or the substrate further comprises an adhesion promoter in a layer on the surface of the polymeric base layer for receiving the coating solution. A process,
b) removing the solvent to form a heat seal layer containing the PLA polymer,
The polymeric base layer comprises a polyethylene terephthalate layer;
The adhesion promoter is an ethylene copolymer or a copolyester resin derived from one or more glycols, at least one aromatic dicarboxylic acid, and at least one aliphatic dicarboxylic acid, and
The method wherein the heat seal layer has a thickness in the range of 0.5 to 10 microns. A method for producing a multilayer film for use in sealing a container,
a) applying a coating solution to a substrate comprising a polymeric base layer,
The coating solution includes a solvent and a PLA polymer;
The substrate further comprises an adhesion promoter in a layer on the surface of the polymeric base layer for receiving the coating fluid ;
b) removing the solvent to form a heat seal layer containing the PLA polymer;
Including
Applying said coating liquid, it sees contains the step of applying the coating liquid to the surface with the adhesion promoter,
The polymeric base layer comprises a polyethylene terephthalate layer;
The adhesion promoter is an ethylene copolymer or a copolyester resin derived from one or more glycols, at least one aromatic dicarboxylic acid, and at least one aliphatic dicarboxylic acid, and
The method wherein the heat seal layer has a thickness in the range of 0.5 to 10 microns .   The method of claim 2, wherein the adhesion promoter comprises a copolyester.   The method of claim 3, wherein the polymeric base layer comprises a biaxially oriented polyethylene terephthalate layer.   The method of claim 1, wherein the coating liquid comprises the adhesion promoter.   The method of claim 5, wherein the adhesion promoter comprises a copolyester.   The method of claim 1, wherein the heat seal layer has a thickness in the range of 2.0 to 10 microns.   The method of claim 2, wherein the copolyester is a heat-sealable copolyester.   The method of claim 1, wherein the PLA polymer is crystalline up to 50%.   The method of claim 1, wherein the PLA polymer is amorphous.   The method of claim 1, wherein the PLA polymer is a PLA homopolymer or a PLA copolymer.   The method of claim 1, wherein the coating liquid further comprises an antifogging agent.   The method of claim 1, further comprising, after step b), step c) of applying an antifogging agent to the heat seal layer.